Method for isotropic etching of copper

ABSTRACT

Copper and copper alloys are etched to provide uniform and smooth surface by employing an aqueous composition that comprises an oxidant, a mixture of at least one weak complexant and at least one strong complexant for the copper or copper alloy, and water and has a pH of about 6 to about 12 so as to form an oxidized etch controlling layer and to uniformly remove the copper or copper alloy; and then removing the oxidized etch controlling layer with a non-oxidizing composition. Copper and copper alloy structure, having smooth upper surfaces are also provided.

This application is a Divisional of U.S. application Ser. No. 10/664,017filed Sep. 17, 2003.

DESCRIPTION

1. Technical Field

The present invention relates to a process for etching copper and copperalloys, and particularly isotropic etching to provide uniform and smoothcopper surfaces. The present invention is also concerned with copper oralloy structures exhibiting uniform and smooth copper surfaces.

2. Background of the Invention

In the fabrication of thin film wiring for electronic applications, itis often required to etch polycrystalline copper surfaces. Anyroughening of this surface can cause significant process or electricalvariability to the structures. Current etchants show significant surfaceroughening, as well as dependence of etching rates on feature density,size, electrical connectivity, and location on the wafer. In particular,commonly used copper etchants, such as acid solutions of peroxide orpersulfate, tend to preferentially etch the copper in the immediateproximity of grain boundaries. In addition, different exposed crystalfaces tend to etch at different rates.

Numerous applications in semiconductor fabrication would benefit frombeing able to provide smooth, sub-micron recess etching of copper andcopper alloys. Some applications in semiconductor fabrication that wouldbenefit for such a process include:

-   -   (1) Selective capping in advanced CMOS devices: to decrease the        effective dielectric constant of the intra-layer insulator, and        also to increase the strength of the via-to-line junctions.    -   (2) Post-CMP (chemical mechanical polishing) clean for copper        Dual Damascene builds: to suppress dendrite growth for increased        reliability, and to remove copper residues on dielectric to        decrease current leakage and increase shorts yield. Although        commercial cleaning solutions exist for this, these are usually        extremely costly.    -   (3) Anchored vias (inverted mushroom): to increase mechanical        strength of via structure.    -   (4) Post-CMP cleanup for FBEOL selective (Ni, Au) plating on        copper—maskless technology, whereby the processing does not        roughen the copper seed layer in the features where the        subsequent plating will be done, while allowing the complete        removal of copper left from the CMP process from the top        surfaces.    -   (5) Post-CMP cleanup for deep via selective Cu plating—system on        a chip.

Accordingly, a great need exists for providing a process for isotropic,smooth sub-micron etching of copper and copper alloys.

SUMMARY OF INVENTION

The present invention addresses problems in the prior art and provides aprocess that is capable of isotropically etching copper and copperalloys to produce smooth copper and copper alloy surfaces.

In particular, one aspect of the present invention is directed to aprocess for etching copper and copper alloys which comprises:

-   -   (a) contacting an exposed copper or copper alloy surface with an        aqueous etching composition that comprises an oxidant, a mixture        of at least one weak complexant and at least one strong        complexant for the copper or copper alloy, and water and has a        pH of about 6 to about 12 so as to form an oxidized etch        controlling layer of a copper compound and to remove the copper        or copper alloy; and    -   (b) then contacting the structure with a non-oxidizing        composition for removing the oxidized etch controlling layer.

The present invention is also concerned with an etched copper or copperalloy surface obtained by the above process.

A further aspect of the present invention is concerned with a processfor generating copper or copper alloy electrical interconnects orcontact pads which comprises:

a. depositing a blanket copper or copper alloy film on a dielectricsubstrate:

b. depositing a thin film or photoresist over the copper or copper alloyfilm,

c. exposing and developing the photoresist through a mask designed togenerate the negative image of the desired copper or copper alloypattern;

d. etching away the copper or copper alloy exposed in c by the abovedisclosed process; and

e. stripping the resist to reveal the desired copper or copper alloypattern.

Another aspect of the present invention relates to a copper structurecomprising a copper or copper alloy surface with an oxidized etchcontrolling layer having a uniform thickness of at least about 0.5nanometers and more typically about 5 nanometers to about 1000nanometers adhered to the copper or copper alloy surface.

A still further aspect of the present invention is concerned with adielectric-copper or copper alloy structure comprising copper or alloythereof being uniformly recessed relative to the top of surroundingdielectric material and having an upper surface with an averageroughness of 3 nanometers or less.

The present invention also relates to an aqueous etching compositionthat comprises an oxidant, a mixture of at least one weak complexant andat least one strong complexant for the copper or copper alloy, and waterand has a pH of about 6 to about 12.

Other objects and advantages of the present invention will becomereadily apparent by those skilled in the art from the following detaileddescription, wherein it is shown and described preferred embodiments ofthe invention, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects,without departing from the invention. Accordingly, the description is tobe regarded as illustrative in nature and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate etch depth as a function of time forcompositions according to the present invention.

FIG. 3 illustrates etch rate as a function of peroxide/ammonia ratio.

FIG. 4 is an AFM surface topograph of copper wires after cleaning with adeaerated IPA/HCl mixture to remove CMP contaminants.

FIG. 5 is an AFM surface topograph of copper lines after the oxidizingetch step according to the present invention.

FIG. 6 is an AFM surface topograph of copper lines after removal of theoxidized layer according to the present invention.

FIG. 7 is an AFM surface topograph of a copper pad after cleaning with adeaerated IPA/HCl mixture, followed by an oxidizing etch step accordingto the present invention and then removal of the oxidized layeraccording to the present invention.

FIG. 8 is an AFM surface topograph of a copper pad after etching in anetchant outside the scope of this invention.

BEST AND VARIOUS MODES FOR CARRYING OUT INVENTION

According to the present invention, copper and copper alloys arecontacted with an aqueous etching composition that comprises an oxidant,a mixture of at least one weak complexant and at least one strongcomplexant for the copper or copper alloy and water and has a pH ofabout 6 to about 12 so as to form an oxidized etch controlling layer ofa copper compound and to remove the copper or copper alloy. The use ofthe etchant of the present invention makes possible the uniform removalof the copper or copper alloy.

Suitable oxidants include peroxide such as hydrogen peroxide, peroxycarboxylate, perborate, and percarbonate. Mixtures of oxidants can beemployed, if desired.

The preferred oxidant is hydrogen peroxide. The amount of oxidant istypically about 0.05 wt % to about 10 wt % and preferably about 2 wt %to about 4 wt %.

The weak complexant typically has a cumulative stability constant withcopper of ≧10¹⁴. Examples of weak complexants for copper and copperalloys are ammonia; amines such as ethylamine, methylamine,tetramethylammonium hydroxide and 2-hydroxyethyl-trimethylammoniumhydroxide.

The strong complexant typically has a cumulative stability constant withcopper of ≦10¹⁵. Examples of strong complexants for copper and copperalloys are aminocarboxylates and aminophosphonates, and morespecifically, 1,2-cyclohexane diaminetetraacetic acid (CDTA), ethylenediamine tetraacetic acid (EDTA), triethylenetetraaminehexaacetic acid;diethylene triaminepentaacetic acid;2,2-dimethyl-1,3-diaminopropane-N,N,N′,N′-tetraacetic acid; cis,cis,cis-3,5-dimethyl-1,2-diaminocyclopentane-N,N,N′,N′-tetraacetic acidand cis-bicyclo (2.2.2) octane-2,3-diamine-N,N,N′,N′-tetraacetic acid.

The preferred weak complexant is ammonia, typically added as aconcentrated ammonium hydroxide solution.

The Molar concentration of the weak complexant is typically about 0.1Molar to about 0.8 Molar and preferably about 0.2 Molar to about 0.4Molar.

The preferred strong complexants are CDTA (see U.S. Pat. No. 6,121,085)and DTPMP (H. Saloniemi & al., 200^(th) ECS meeting extended abstracts,2001), due to their stability against oxidation by peroxide, and EDTA,with CDTA and DTPMP being most preferred. The strong complexant istypically present in amounts of about 0.001 to about 10 g/l.

According to more preferred aspects of the present invention, thecomplexant comprises ammonia along with CDTA or EDTA which act asstabilizers.

The use of a combination of both the weak complexant and strongcomplexant makes possible a relatively steady state regime of continuousinhibiting formation and dissolution. It is believed that the presenceof the strong complexant insures a continuous slow dissolution of theinhibiting layer, which in turn makes possible to avoid a multipleetching step process for dissolving the inhibiting layer and thencontacting the structure again with the etchant. The etching process ofthis invention can be carried out in a single etching step. On the otherhand, the use of only a strong complexant, the inhibiting layer wouldnot be adequately formed and the etching would tend to be less uniform.

The etching composition typically has a pH of about 6 to about 12 andmore typically a basic pH. The pH can be adjusted to the desired levelby adding a non-oxidizing acid such as sulfuric acid, acetic acid ormethanesulfonic acid; or a base such as sodium hydroxide, potassiumhydroxide and tetramethyl ammonium hydroxide.

A specific composition employed according to the present invention has avolume ratio of 40:2:1 v/v H₂O: H₂O₂ 30%: NH₄OH 56.6% (i.e., an aqueoussolution containing 1.55 wt % H₂O₂ and 0.57 wt % NH₃) and 0.05% CDTA,with the pH adjusted downward to 9.5 (by the addition of sulfuric acid),so as to ensure formation of the inhibiting layer. Another suchcomposition has a volume ratio of 40:4:1 v/v H₂O:H₂O₂ 30%: NH₄OH 56.6%(i.e., an aqueous solution containing an aqueous solution containing2.94 wt % H₂O₂ and 0.54% NH₃) and 0.5% CDTA and a pH of approximately10.2. In this higher-oxidant case no pH adjustment is necessary for theformation of the inhibiting layer.

The component concentrations and operating temperature are judiciouslyselected so that contacting of the copper or copper alloy with thecomposition results in a uniform inhibiting or etch control layer.Dissolution of the inhibiting layer in acid generates recesses ofuniform depth and smooth, flat copper surfaces.

It is believed that the inhibiting or etch control layer formed in situis typically a hydrated copper oxide. The inhibiting layer formationthen limits the diffusion of the oxidant towards the copper metalsurface, and the diffusion of the copper ionic species away from themetal surface to govern the overall reaction rate. By creating thisinhibiting layer the surface layer the copper or copper alloy can beselectively removed thus resulting in a very uniform etching. Thecopper-complexing components of the solution attack the exposed surfaceof the inhibiting layer and remove it at a rate which depends on theirconcentrations. The thickness of the inhibiting layer, and the etchrate, can be controlled by modifying the concentrations of the oxidantand the complexants, as well as the temperature.

Unlike passivation layers, such as the well known ones formed bybenzotriazole (BTA), the inhibiting layer, according to the presentinvention, does not prevent oxidation of the metal. Instead, itmodulates the oxidation process by allowing substantial diffusion ofetchant toward the copper surface. Since the reaction of the oxidantwith copper is very fast, the overall etching rate is controlled bydiffusion of reactants and possibly reaction products through theinhibiting layer, which at a given time is of about the same thicknesseverywhere irrespective of copper feature size.

At the same time, electrochemical reactions of the galvanic corrosiontype, which in state-of-the-art etchants etch the most active metalliccopper areas (e.g., small features) selectively, are suppressed. Sincediffusion through the inhibiting layer is much slower than in theliquid, effects of local hydrodynamic variations are also lessened.

The thickness of the inhibiting layer is a function of etchingconditions. The layer is formed continuously at the copper-inhibitinglayer interface, while also being dissolved continuously at theinhibiting layer-liquid interface. The relative rates of these tworeactions determine its thickness at any given time. A typical thicknessof the inhibiting layer is about 2 nanometers to about 1000 nanometers.

Generally, the etching rate increases as the pH and/or concentrations ofthe complexants such as ammonia and CDTA increases. On the other hand,this rate decreases as the oxidant such as peroxide content increases,in marked contrast to the etching rate by acid-peroxide mixtures. Whenthe etch is used in a recirculating or a static tool, the presence ofthe stronger complexant for Cu(2+) is desirable in order to preventCu(2+)-catalyzed H₂O₂ decomposition and the resulting oxygen bubbling.This bubbling tends to cause defects.

The etching rate is also increased by increasing temperature. Forexample, raising the etch temperature form 25 to 65° C. increases theetch rate by a factor of 6, without negatively affecting the etchuniformity.

FIG. 1 shows the etch depth in nanometers as a function of time for aroom temperature etch using a composition (composition A) having avolume ratio of 40:2:1 v/v H₂O: H₂O₂ 30%:NH₄OH 56.6% (i.e., an aqueoussolution containing 1.55 wt % H₂O₂ and 0.57 wt % NH₃) and 0.5 g/l CDTAand pH adjusted downward to 9.5 (by addition of sulfuric acid) so as toensure formation of the inhibiting layer.

It is noted that the rate stabilizes after an initiation period.

FIG. 2 shows the etch depth in nanometers as a function of time for aroom temperature etch using a composition (composition B) having avolume ratio of 40:4:1 v/v H₂O: H₂O₂ 30%: NH₄OH 56.6% (i.e., an aqueoussolution containing an aqueous solution containing 2.94 wt % H₂O₂ and0.54% NH₃) and 0.5 g/l CDTA and a pH of approximately 10.2; in thishigher-oxidant case no pH adjustment is necessary for the formation ofthe inhibiting layer. The etch rate stabilizes after the initiationperiod. Compared to the example shown in FIG. 1, the etch rate isslower. Etching is slower in this case, due to the higherperoxide/ammonia ratio, an effect shown in a more general way in FIG. 3.In FIG. 3, the results of 10-minute etching in 40:4:x v/v solutions(x=volume of concentrated ammonia) are displayed as a function of x.Note that, (a) the etch depth is approximately linearly dependent onammonia concentration, and (b) the inhibition layer (measured separatelyin each case before removal) is in all cases thicker than the copper itreplaces.

Typically, at the end of the etching process the remaining copper iscovered by a substantial inhibiting layer, often as thick or thickerthan the copper it has replaced. This layer needs to be removed. It isnoteworthy, though, that the removal does not have to be immediate; infact, the sample can be rinsed and dried at this stage and then storedfor several days without significant effect on the eventual surfacequality.

The inhibiting layer is removed by exposing the surface to anon-oxidizing solution capable of dissolving hydrous copper oxides, suchas an acid solution or a solution containing a copper complexant such asglycine or imidazole. The dissolving solution is preferably deaerated soas to prevent any additional, and non-uniform, etching by dissolvedoxygen. Alternatively, an acid solution, e.g., dilute sulfuric acid,that contains a corrosion inhibitor such as BTA can be used. The acidcomponent readily dissolves the inhibiting layer, while dissolved oxygenwith the BTA forms a passive film preventing oxygen-driven corrosion.

Finally, the acid can be rinsed away with deionized water, preferablydeaerated, optionally followed by a water miscible solvent, and thesample can be dried by a commonly used technique (by blowing nitrogen,in a Marangoni dryer, etc.).

Typical non-oxidizing acids are sulfuric acid, hydrochloric acid, aceticacid and methanylsulfonic acid.

A typical composition used contains about 0.2 Molar acetic acid.

The present invention makes possible uniform removal of 5 nanometers toabout 1000 nanometers and more typically about 10 nanometers to about500 nanometers. For instance, examples using the in-situ formedinhibiting layer on blanket deposited copper and patterned electroplatedcopper, after CMP (chemical-mechanical patterning) provided:

-   -   5 nanometers attainable with a 30 second process, giving        slightly reduced copper height differences at grain boundaries    -   15-20 nanometers etch completely removes height differences at        grain boundaries;    -   300 nanometers etch, demonstrated on blanket electroplated        copper, results in mirror finish.

Remarkably, beyond a certain minimal etch depth (20-40 nanometers) theresulting low surface roughness reaches a steady-state condition andbecomes independent of the etch depth.

With respect to electrical interconnects, the main prior art challengeis to prevent self-induced galvanic corrosion. An example system is apatterned structure where a wide wire with large grains is electricallyor directly connected to a narrow wire with small grains. An acidetchant applied to such a structure tends to selectively oxidize andremove copper with the highest energy. In the example structure, thewide wire could drive preferential dissolution of the narrow wire. Theinhibiting layer formed by the etchant in this invention equalizes thecopper surface energy, thus preventing selective corrosion.

The etching process of the present invention yields much betteruniformity of etching than existing methods, both on a micro scale(between features or parts of features) and on a wafer scale. Transportthrough the inhibiting layer, rather than through the much thickerliquid surface diffusion layer, or through the solution bulk, definesthe etching rate. Therefore, the local density of features or shape offeatures (at the liquid diffusion layer scale) has little effect, andthe same is true for the intensity of agitation, whose lack ofuniformity across the wafer often causes uneven etching in other etchingprocesses. Various methods of agitation can be employed, with thefixtured wafer rotating in a stationary solution, stationary wafers in astream of etching solution running in a recirculation loop, etc.However, a minimum rate of agitation is necessary to achieve uniformity.For example, when etching a 200 mm wafer in a rotating fixture inside astationary solution, a rotation rate of at least about 30 rpm andpreferably 100 rpm is advisable.

The following non-limiting examples are presented to further illustratethe present invention.

EXAMPLE 1

An interconnect copper structure, which includes a dielectric and aliner inert to the etchant and containing 1 and 0.1 micron wide wires,was first cleaned with a deaerated isopropanol/HCl mixture (25% IPA,0.18% HCl) to remove any contaminants from the preceding CMP(chemical-mechanical polishing) step, and then was etched for about 4minutes at room temperature in an etchant of this invention (an aqueoussolution containing 2.94 wt % H₂O₂, 0.54% NH₃, and 0.05% CDTA and a pHof approximately 10.2). During the etching the sample was stationary ina beaker and the solution was stirred with a 2.5 cm magnetic stirringbar at 180 rpm. The sample was then dried in a nitrogen stream. Theinhibiting layer was then removed by treating the sample for about 4minutes with a nitrogen-deaerated 100:1 (v/v) acetic acid solution.

This example illustrates the steps of inhibiting layer formation anddissolution with respect to effects on copper recessing. See FIGS. 4, 5and 6 which show AFM (atomic force microscope) images of the sameinterconnect copper structure taken after each step in the copperetching process. These figures are of the same exact area on the samesample.

FIG. 4 is the AFM after CMP and IPA/HCl clean. The dielectric has asmooth appearance and lighter shading; while the copper wires havetexture and appear in darker shading showing the copper lying below thedielectric surface. The average depth of the copper 1 micron wires belowthe dielectric surface is about 6 nanometers. The AFM imaging of the 1micron copper wires shows copper grains and some defects. The averagedepth of the copper 0.1 micron wires below the dielectric surface isabout 4 nanometers. The copper roughness and depth below the dielectricis a typical result of CMP and IPA/HCl treatment.

FIG. 5 is the AFM image taken after a 4 minute etch according to thepresent invention, on the same exact interconnect structure of FIG. 4,with the “hydrated copper oxide” inhibiting layer not yet removed (waterrinsed and dried). The inhibiting layer on the copper wires is formed bythe etch and extends above the dielectric by about 10 nanometers forboth 1 micron and 0.1 micron wires (lighter shade in this image). Thegrain structure and defects of the copper in the 1 micron wire noted inFIG. 4 are not visible in FIG. 5.

FIG. 6 is the AFM image taken after the “hydrated copper oxide”inhibiting layer was removed with dilute acetic acid; on the same exactinterconnect structure of FIG. 4. The average depth for both the 1micron and the 0.1 micron wires below the dielectric surface was about26 nanometers.

EXAMPLE 2

A substrate similar in type to the one used in Example 1, was cleaned asdescribed above and then was etched for 8 minutes in the same etchingsolution as used in Example 1 and under the same conditions as above.The inhibiting layer was immediately removed by treating the sample forabout 2 minutes with a nitrogen-deaerated mixture of 0.2 Molar sulfuricacid and 0.2 Molar acetic acid.

This example demonstrates the possibility of deeper recesses which inturn shows that the etch according to the present invention is not selflimiting as is the known art. This example also demonstrates that thepresent invention makes possible smoother copper recesses than typicaletchants as, for instance, exemplified in Example 3 below.

The results are shown in FIG. 7. FIG. 7 is an AFM image of a 3×5 microncopper pad imbedded in a dielectric after processing with CMP andIPA/HCl clean, followed by an 8 minute etch according to the presentinvention and the as acid removal of the inhibiting layer. The averagedepth of the copper below the dielectric surface is about 52 nanometers,with a roughness about the same as obtained in the etch of example (seeFIG. 6).

EXAMPLE 3

A sample similar in type to the one used in Example 2 was etched in astandard Cu etch (H₂O:H₂O₂ 30%: acetic acid 1000:3:5 v/v). The averagedepth of the copper below the dielectric surface is about 54 nanometers.Note the roughness that occurs due to the non-uniform copper removal(AFM surface topograph, FIG. 8) as compared to the smooth copper surfaceachieved by the present invention (see FIGS. 6 and 7).

The foregoing description of the invention illustrates and describes thepresent invention. Additionally, the disclosure shows and describes onlythe preferred embodiments of the invention but, as mentioned above, itis to be understood that the invention is capable of use in variousother combinations, modifications, and environments and is capable ofchanges or modifications within the scope of the inventive concepts asexpressed herein, commensurate with the above teachings and/or the skillor knowledge of the relevant art. The embodiments described hereinaboveare further intended to explain best modes known of practicing theinvention and to enable others skilled in the art to utilize theinvention in such, or other, embodiments and with various modificationsrequired by the particular applications or uses of the invention.Accordingly, the description is not intended to limit the invention tothe form disclosed herein. Also, it is intended that the appended claimsbe construed to include alternative embodiments. All publications andpatent applications cited in this specification are herein incorporatedby reference as if each individual publication or patent applicationwere specifically and individually indicated to be incorporated byreference.

1. An etched copper or copper alloy surface obtained by the processwhich comprises: a) contacting an exposed copper or copper alloy surfacewith an aqueous etching composition that comprises an oxidant, a mixturecomprising at least one weak complexant for the copper or copper alloyhaving a cumulative stability constant with copper of ≦10¹⁴ and at leastone strong complexant for the copper or copper alloy having a cumulativestability constant with copper of ≧10¹⁵, and water and has a pH of about6 to about 12 so as to form an oxidizable etch controlling layer of acopper compound 2, and to remove the copper or copper alloy; and b) thencontacting the structure with a non-oxidizing composition for removingthe oxidizable etch controlling layer.
 2. A copper structure comprisingcopper or copper alloy surface and an oxidized etch controlling layer,the etch controlling layer having a uniform thickness of about 2 toabout 1000 nanometers and adhered to the copper or copper alloy surface.3. The structure of claim 2 wherein the etch controlling layer is ahydrated copper oxide layer.
 4. The structure of claim 2 wherein theetch controlling layer is obtained by contacting an exposed copper orcopper alloy surface with an aqueous etching composition that comprisesan oxidant, a complexant for the copper or alloy, and water and has a pHof about 6 to about
 12. 5. The structure of claim 2 being coppercontaining electrical interconnects or contact pads.
 6. The structure ofclaim 2 wherein the copper or alloy is recessed relative to the top ofsurrounding dielectric material.
 7. A dielectric-copper or copper alloystructure comprising copper or alloy thereof conformally recessedrelative to the top of surrounding dielectric material, and having asurface with an average roughness of about 3 nanometers or less.
 8. Thestructure of claim 7 wherein the copper or alloy thereof has a thicknessof at least about
 5. 9. An aqueous etching composition having a pH ofabout 6 to about 12 and comprising about 0.5 to about 10 wt % of anoxidant; a mixture comprising at least one weak complexant for thecopper or copper alloy having a cumulative stability constant withcopper of ≦10¹⁴ and at least one strong complexant for the copper orcopper alloy having a cumulative stability constant with copper of≧10¹⁵, the amount of the at least one weak complexant is about 0.1 Molarto about 0.8 Molar, and the amount of the at least one strong complexantis about 0.001 to about 10 g/l; and water.
 10. The etching compositionof claim 9 which comprises at least one peroxide compound and at leastone weak complexant for copper or copper alloy selected from the groupconsisting of ammonia and an amine; and at least one strong complexantfor the copper or copper alloy selected from the group consisting of anaminocarboxylate and an aminophosphonate; and has a basic pH.
 11. Theetching composition of claim 10 wherein the peroxide is selected fromthe group consisting of hydrogen peroxide, a peroxy carboxylate,perborate, and percarbonate, and mixtures thereof.
 12. The etchingcomposition of claim 11 wherein the at least one weak complexant isselected from the group consisting of ammonia, ethylamine, methylamine,tetramethylammonium hydroxide and 2-hydroxyethyl-trimethylammoniumhydroxide; and the at least one strong complexant is selected from thegroup consisting of 1,2-cyclohexane diaminetetraacetic acid (CDTA),ethylene diamine tetraacetic acid (EDTA),triethylenetetraaminehexaacetic acid; diethylene triaminepentaaceticacid; 2,2-dimethyl-1,3-diaminopropane-N,N,N′,N′-tetraacetic acid; cis,cis,cis-3,5-dimethyl-1,2-diaminocyclopentane-N,N,N′,N′-tetraacetic acidand cis-bicyclo (2.2.2) octane-2,3-diamine-N,N,N′,N′-tetraacetic acid.13. The etching composition of claim 9 wherein the oxidant compriseshydrogen peroxide and said complexant comprises ammonia.
 14. The etchingcomposition of claim 13 which comprises about 0.001-10 g/l of1,2-cyclohexane diaminotetraacetic acid, ethylene diamine tetraaceticacid or both.
 15. The etching composition of claim 9 which comprisesabout 1.5 wt % hydrogen peroxide, about 0.5 wt % ammonia and about 0.5g/l of 1,2-cyclohexane-diaminotetraacetic acid.
 16. The etchingcomposition of claim 9 which comprises about 3 wt % hydrogen peroxide,abut 0.5 wt % ammonia and about 0.5 g/l of 1,2-cyclohexanediaminetetraacetic acid.
 17. The etching composition of claim 9 whichfurther comprises a non-oxidizing acid or salt thereof or a base. 18.The etching composition of 17 wherein the non-oxidizing acid is selectedfrom the group consisting of sulfuric acid, hydrochloric acid, aceticacid and methanesulfonic acid and mixtures thereof and said base isselected from the group consisting of sodium hydroxide, potassiumhydroxide, and tetramethyl ammonium hydroxide and mixtures thereof. 19.The etching composition of claim 9 which comprises a deaeratednon-oxidizing aqueous acid.